Author: Gjalt-Jorn Peters

Gjalt-Jorn Peters works at the Dutch Open University, where he teaches methodology and statistics, and does research into health psychology, specifically behavior change, in general and applied to nightlife-related risk behavior. He is involved in Dutch nightlife prevention project Celebrate Safe, where he is responsible for the Party Panel study. In addition, he maintains the userfriendlyscience, ufs, and behaviorchange R packages. An overview of his academic publications is available here.

On the 25th August 2018, the book “The Netherlands and synthetic drugs” by Pieter Tops, Judith van Valkenhoef, Edward van der Torre and Luuk van Spijk was published. In this book, the authors calculated that in the Netherlands, annually 971 566 879 XTC pills are produced, 80% of which is exported. This book prompted many reactions, and the authors responded to these again by recalculating the export percentage. In this blog post I respond by calculating how much XTC the world uses every year, a number that implies that the export percentage was not what was incorrect, but the total production estimate.

Recently, a report came out (“Waar een klein land groot in kan zijn”) by Pieter Tops, Judith van Valkenhoef, Edward van der Torre and Luuk van Spijk (all employed by the Dutch Police Academy) drawing two sensational conclusions. First, that every year, the Netherlands produces € 18 916 882 439 (18,9 billion) worth of synthetic drugs. Second, that in the Netherlands, every year 194 313 376 ecstasy pills are used. This latter conclusions is clearly wrong, which sheds doubt on the veracity of the former. Both the original report and the abbreviated version are written in a sensationalist tone; might the authors have neglected to verify their impressive conclusions with sufficient rigor?

In health psychology, there exists a lack of conceptual clarity regarding a number of terms that are at the core of psychological science. True, this problem exists in psychology in general, but the terms Behavior Change Technique (from the BCT taxonomy approach) and Method for Behavior Change (from the Intervention Mapping approach) have exacerbated matters within behavior change science. In this post, I will discuss this in more detail, based on a recent Twitter discussion that erupted around whether a psychological variable targeted by a behavior change technique is a mediator or not:

Where by 'mediators', you mean 'determinants' I guess? I don't think 'mediator' is the right term – there is no predictor variable. A manipulation is an operationalisation of a construct – if the manipulation is valid, the construct changes, *that* is the variable, the predictor.